1. Field of the Invention
The invention relates to an AC/DC converting circuit and a starting method thereof. More particularly, the invention relates to an AC/DC converting circuit that shortens a starting time of the AC/DC converting circuit and a starting method thereof.
2. Description of Related Art
In the conventional techniques, before an AC/DC converting circuit is started, an AC/DC power conversion controller in the AC/DC converting circuit is continuously detecting a voltage value of an inputted AC voltage. As shown in a schematic view illustrating a waveform of an AC voltage and a power source voltage of an AC/DC power conversion controller of FIG. 1, since a power source current needed for the AC/DC power conversion controller to perform an AC voltage detection is greater than a current supplied by an AC voltage source, the power source voltage of the AC/DC power conversion controller dropped down due to an insufficient voltage supply.
When the power source voltage of the AC/DC power conversion controller drops down to a triggered voltage level V1 of a voltage lockout, a voltage detection function of the AC/DC power conversion controller is disabled. At this time, a current needed by the AC/DC power conversion controller is smaller than that supplied by the AC voltage source. Thus, the power source voltage of the AC/DC power conversion controller gradually rises, and then the AC/DC power conversion controller begins to detect the AC voltage after the power source voltage of the AC/DC power conversion controller gradually rises up to a released voltage level V2 of the voltage lockout. Thus, the AC voltage is repeatedly detected until the AC voltage rises up to a start-up voltage, which causes a saw tooth wave change of the power source voltage of the AC/DC power conversion controller as shown in FIG. 1.
In a conventional way of starting an AC/DC converting circuit, a power source voltage of an AC/DC power conversion controller has to oscillate greatly back and forth between the triggered voltage level V1 and the released voltage level V2 of the voltage lockout. Even if the AC voltage rises up to the start-up voltage, a waiting time is still needed for the power source voltage of the AC/DC power conversion controller to rise up to the released voltage level V2 of the voltage lockout in order to start the AC/DC converting circuit. However, a starting speed of the AC/DC converting circuit is thus slowed down.